The development of synthetic dental materials by Rafael L. Bowen disclosed in U.S. Pat. No. 3,066,112 was of great importance. Bowen disclosed the use of the reaction products of glycidylacrylate and glycidylmethacrylate with bisphenols and particularly the reaction product of glycidylmethacrylate and bisphenol. A (Bis-GMA) in place of the methylmethacrylate which was used up to that time. These resins were used to form compositions which also contained quartz glass treated with a vinyl silane present as an inorganic filler.
Since that time a great number of monomers suitable as bonding agents when polymerized have been disclosed. Inorganic filling materials have also been disclosed. The art has also disclosed catalysts and catalyst systems for the polymerization of the resin components to provide improved dental materials, see for example German Disclosure documents 15 70 971; 23 12 258; 23 12 559; 24 19 887; 26 58 538; 28 56 550; German Pat. No. 23 47 591; and U.S. Pat. Nos. 3,721,644; 3,799,905; and 4,028,325.
The polymerized resin which forms the binder of the dental compositions has shrinkage characteristics and coefficient of thermal expansion characteristics which are high when compared to the corresponding characteristics of hard tooth tissues. The inclusion of inorganic fillers in the dental composition reduces the differences. The compositions which contain the inorganic fillers also have higher compressive strength.
The early synthetic dental compositions could be polished to a high luster. However the synthetics containing the fillers which were first used could not be polished to a high luster. Fillers are now known which can be polished to a high luster and therefore provide aesthetically satisfactory dental artifacts such as dental fillings and dental prosthetics as disclosed in U.S. Pat. No. 4,029,632.
The synthetic dental materials prepared by polymerizing resins are transparent to X-rays and therefore do not show up on X-ray film. Inorganic fillers may also be useful to make the composition opaque to such radiation and therefore cause the set dental composition in the tooth to become visible when exposed to X-rays. U.S. Pat. No. 3,539,526 discloses a fine-grained glass made up of SiO.sub.2, BaF.sub.2, Al.sub.2 O.sub.3 and B.sub.2 O.sub.3 as a filler for dental compositions which imparts X-ray opacity to the composition.
U.S. Pat. No. 3,959,212 discloses a similar X-ray opaque filler for dental compositions comprising a crystalline barium silicate (Ca.sub.2 Ba(SiO.sub.3).sub.3, BaAl.sub.2 Si.sub.2 O.sub.8, and BaMgCa.sub.2 Si.sub.2 O.sub.8). U.S. Pat. No. 4,215,033 discloses a semi-porous filler formed from a two phase glass composed of SiO.sub.2, B.sub.2 O.sub.3, Al.sub.2 O.sub.3 and SrO, wherein one of the phases is removed to form the porous surface.
It is an object of the present invention to provide dental compositions which when polymerized set to form dental fillings and other prosthetic dental artifacts which contain a fine grained filler and which are opaque to X-rays and which, after setting (curing) have high compressive strength and good abrasion resistance as well as the ability to polish up to form a high gloss comparable to that which may be formed on a cured synthetic which does not contain filler.